8-Speed Transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes four planetary gear sets, five torque-transmitting devices, one grounded member and three fixed interconnections. The powertrain includes an engine and torque converter that is continuously connected to one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The five torque-transmitting devices provide interconnections between various gear members, and the transmission housing, and are operated in combinations of two to establish eight forward speed ratios and one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission having fourplanetary gear sets that are controlled by five torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five- or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedtransmission having four planetary gear sets controlled to provide eightforward speed ratios and one reverse speed ratio.

The transmission family of the present invention has four planetary gearsets, each of which includes a first, second and third member, whichmembers may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order.

In referring to the first, second, third and fourth gear sets in thisdescription and in the claims, these sets may be counted “first” to“fourth” in any order in the drawing (i.e., left to right, right toleft, etc.). Additionally, the first, second or third members of eachgear set may be counted “first” to “third” in any order in the drawing(i.e., top to bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

A first interconnecting member continuously connects the second memberof the first planetary gear set with the first member of the secondplanetary gear set.

A second interconnecting member continuously connects the third memberof the first planetary gear set with the third member of the thirdplanetary gear set.

A third interconnecting member continuously connects the second memberof the second planetary gear set with the second member of the thirdplanetary gear set and with the third member of the fourth planetarygear set.

The input member is continuously connected with the first member of thefourth planetary gear set. The output member is continuously connectedwith the second member of the fourth planetary gear set. The firstmember of the first planetary gear set is continuously connected with astationary member (transmission housing/casing).

A first torque-transmitting device, such as a brake, selectivelyconnects the third member of the second planetary gear set with astationary member (transmission housing/casing).

A second torque-transmitting device, such as a clutch, selectivelyconnects the second member of the first planetary gear set with thesecond member of the fourth planetary gear set.

A third torque-transmitting device, such as a clutch, selectivelyconnects the third member of the second planetary gear set with thefirst member of the third planetary gear set.

A fourth torque-transmitting device, such as a clutch, selectivelyconnects the first member of the third planetary gear set with the firstmember of the fourth planetary gear set.

A fifth torque-transmitting device, such as a clutch, selectivelyconnects the first member of the third planetary gear set with thesecond member of the fourth planetary gear set.

The five torque-transmitting devices are selectively engageable incombinations of two to yield eight forward speed ratios and one reversespeed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is a schematic representation of the powertrain of FIG. 1 adepicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes four planetary gear sets20, 30, 40 and 50.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27, 28 rotatablymounted on a carrier member 29. The pinion gears 27 are disposed inmeshing relationship with the sun gear member 22, and the pinion gears28 are disposed in meshing relationship with both the ring gear member24 and the respective pinion gear 27.

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 rotatablymounted on a carrier member 39 and disposed in meshing relationship withboth the sun gear member 32 and the ring gear member 34.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The planetary gear set 50 includes a sun gear member 52, a ring gearmember 54, and a planet carrier assembly member 56. The planet carrierassembly member 56 includes a plurality of pinion gears 57 mounted on acarrier member 59 and disposed in meshing relationship with both the sungear member 52 and the ring gear member 54.

The planetary gear arrangement also includes five torque-transmittingdevices 80, 82, 84, 85 and 86. The torque-transmitting device 80 is astationary-type torque-transmitting device, commonly termed brake orreaction clutch. The torque-transmitting devices 82, 84, 85 and 86 arerotating-type torque-transmitting devices, commonly termed clutches.

The input member 17 is continuously connected with the sun gear member52 of the planetary gear set 50. The output member 19 is continuouslyconnected with the planet carrier assembly member 56 of the planetarygear set 50. The sun gear member 22 of the planetary gear set 20 iscontinuously connected with the transmission housing 60.

A first interconnecting member 70 continuously connects the planetcarrier assembly member 26 of the planetary gear set 20 with the sungear member 32 of the planetary gear set 30. A second interconnectingmember 72 continuously connects the ring gear member 24 of the planetarygear set 20 with the ring gear member 44 of the planetary gear set 40. Athird interconnecting member 74 continuously connects the planet carrierassembly member 36 of the planetary gear set 30 with the planet carrierassembly member 46 of the planetary gear set 40 and with the ring gearmember 54 of the planetary gear set 50.

A first torque-transmitting device, such as brake 80, selectivelyconnects the ring gear member 34 of the planetary gear set 30 with thetransmission housing 60. A second torque-transmitting device, such asclutch 82, selectively connects the planet carrier assembly member 26 ofthe planetary gear set 20 and the sun gear member 32 of the planetarygear set 30 via interconnecting member 70 with the planet carrierassembly member 56 of the planetary gear set 50. A thirdtorque-transmitting device, such as clutch 84, selectively connects thering gear member 34 of the planetary gear set 30 with the sun gearmember 42 of the planetary gear set 40. A fourth torque-transmittingdevice, such as clutch 85, selectively connects the sun gear member 42of the planetary gear set 40 with the sun gear member 52 of theplanetary gear set 50. A fifth torque-transmitting device, such asclutch 86, selectively connects the sun gear member 42 of the planetarygear set 40 with the planet carrier assembly member 56 of the planetarygear set 50.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting devices are selectively engaged incombinations of two to provide eight forward speed ratios and onereverse speed ratio, all with single transition sequential shifts andone overdrive ratio.

As set forth above, the engagement schedule for the torque-transmittingdevices is shown in the truth table of FIG. 1 b. The chart of FIG. 1 bdescribes the ratio steps that are attained in the above describedtransmission. For example, the step ratio between the first and secondforward speed ratios is 1.53, while the step ratio between the reversespeed ratio and first forward ratio is −0.76.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format. A lever diagram is aschematic representation of the components of a mechanical device suchas an automatic transmission. Each individual lever represents aplanetary gearset, wherein the three basic mechanical components of theplanetary gear are each represented by a node. Therefore, a single levercontains three nodes: one for the sun gear member, one for the planetgear carrier member, and one for the ring gear member. The relativelength between the nodes of each lever can be used to represent thering-to-sun ratio of each respective gearset. These lever ratios, inturn, are used to vary the gear ratios of the transmission in order toachieve appropriate ratios and ratio progression. Mechanical couplingsor interconnections between the nodes of the various planetary gear setsare illustrated by thin, horizontal lines and torque transmittingdevices such as clutches and brakes are presented as interleavedfingers. If the device is a brake, one set of the fingers is grounded.Further explanation of the format, purpose and use of lever diagrams canbe found in SAE Paper 810102, authored by Benford, Howard and Leising,Maurice, “The Lever Analogy: A New Tool in Transmission Analysis”, 1981,which is hereby fully incorporated by reference.

The powertrain 10 includes an input member 17 continuously connectedwith the engine 12, an output member 19 continuously connected with thefinal drive mechanism 16, a first planetary gear set 20A having threenodes: a first node 22A, a second node 26A and a third node 24A; asecond planetary gear set 30A having three nodes: a first node 32A, asecond node 36A and a third node 34A; a third planetary gear set 40Ahaving three nodes: a first node 42A, a second node 46A and a third node44A; and a fourth planetary gear set 50A having three nodes: a firstnode 52A, a second node 56A and a third node 54A.

The input member 17 is continuously connected with the node 52A. Theoutput member 19 is continuously connected with the node 56A. The node22A is continuously connected with the transmission housing 60.

The node 26A is continuously connected with node 32A via interconnectingmember 70. The node 24A is continuously connected with node 44A viainterconnecting member 72. The node 36A is continuously connected withnodes 46A and 54A via interconnecting member 74.

A first torque-transmitting device, such as brake 80, selectivelyconnects the node 34A with the transmission housing 60. A secondtorque-transmitting device, such as clutch 82, selectively connects thenode 26A with the node 56A. A third torque-transmitting device, such asclutch 84, selectively connects the node 34A with the node 42A. A fourthtorque-transmitting device, such as clutch 85, selectively connects thenode 42A with the node 52A. A fifth torque-transmitting device, such asclutch 86, selectively connects the node 42A with the node 56A.

To establish ratios, two torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row of FIG. 1 b. For example, to establishreverse gear, the brake 80 and clutch 85 are engaged. The brake 80engages the node 34A with the transmission housing 60. The clutch 85engages the node 42A with the node 52A. Likewise, the eight forwardratios are achieved through different combinations of clutch engagementas per FIG. 1 b.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second, third and fourth planetary gear sets each havingfirst, second and third members; said first member of said firstplanetary gear set being continuously connected with a stationarymember; a first interconnecting member continuously connecting saidsecond member of said first planetary gear set with said first member ofsaid second planetary gear set; a second interconnecting membercontinuously connecting said third member of said first planetary gearset with said third member of said third planetary gear set; a thirdinterconnecting member continuously connecting said second member ofsaid second planetary gear set with said second member of said thirdplanetary gear set and with said third member of said fourth planetarygear set; and five torque-transmitting devices for selectivelyinterconnecting said members of said planetary gear sets with saidstationary member or with other members of said planetary gear sets,said five torque-transmitting devices being engaged in combinations oftwo to establish at least eight forward speed ratios and at least onereverse speed ratio between said input member and said output member. 2.The transmission of claim 1, wherein a first of said fivetorque-transmitting devices is operable for selectively connecting saidthird member of said second planetary gear set with said stationarymember.
 3. The transmission of claim 2, wherein a second of said fivetorque-transmitting devices is operable for selectively connecting saidsecond member of said first planetary gear set with said second memberof said fourth second planetary gear set.
 4. The transmission of claim3, wherein a third of said five torque-transmitting devices is operablefor selectively connecting said third member of said second planetarygear set with said first member of said third planetary gear set.
 5. Thetransmission of claim 4, wherein a fourth of said fivetorque-transmitting devices is operable for selectively connecting saidfirst member of said third planetary gear set with said first member ofsaid fourth planetary gear set.
 6. The transmission of claim 5, whereina fifth of said five torque-transmitting devices is operable forselectively connecting said first member of said third planetary gearset with said second member of said fourth planetary gear set.
 7. Thetransmission defined in claim 1, wherein said first torque-transmittingdevice comprises a brake, and said second, third, fourth and fifthtorque-transmitting devices comprise clutches.
 8. The transmission ofclaim 1, wherein said first, second and third members of said first,second, third and fourth planetary gear sets comprise a sun gear member,a planet carrier assembly member and a ring gear member, respectively.9. The transmission of claim 1, wherein said input member iscontinuously connected with said first member of said fourth planetarygear set, and said output member is continuously connected with saidsecond member of said fourth planetary gear set.
 10. The transmission ofclaim 1, wherein said second member of said first planetary gear set isa double-pinion carrier.
 11. A multi-speed transmission comprising: aninput member; an output member; first, second, third and fourthplanetary gear sets each having first, second and third members; saidinput member being continuously connected with said first member of saidfourth planetary gear set; and said output member being continuouslyconnected with said second member of said fourth planetary gear set;said first member of said first planetary gear set being continuouslyconnected with a stationary member; a first interconnecting membercontinuously connecting said second member of said first planetary gearset with said first member of said second planetary gear set; a secondinterconnecting member continuously connecting said third member of saidfirst planetary gear set with said third member of said third planetarygear set; a third interconnecting member continuously connecting saidsecond member of said second planetary gear set with said second memberof said third planetary gear set and with said third member of saidfourth planetary gear set; a first torque-transmitting deviceselectively connecting said third member of said second planetary gearset with said stationary member; a second torque-transmitting deviceselectively connecting said second member of said first planetary gearset with said second member of said fourth planetary gear set; a thirdtorque-transmitting device selectively connecting said third member ofsaid second planetary gear set with said first member of said thirdplanetary gear set; a fourth torque-transmitting device selectivelyconnecting said first member of said third planetary gear set with saidfirst member of said fourth planetary gear set; a fifthtorque-transmitting device selectively connecting said first member ofsaid third planetary gear set with said second member of said fourthplanetary gear set; and said five torque-transmitting devices beingengaged in combinations of two to establish at least eight forward speedratios and at least one reverse speed ratio between said input memberand said output member.
 12. The transmission of claim 11, wherein saidfirst, second and third members of said first, second, third and fourthplanetary gear sets comprise a sun gear member, a planet carrierassembly member and a ring gear member, respectively.
 13. A multi-speedtransmission comprising: an input member; an output member; first,second, third and fourth planetary gear sets each having a sun gearmember, planet carrier assembly member and ring gear member; said inputmember being continuously interconnected with said sun gear member ofsaid fourth planetary gear set, and said output member beingcontinuously interconnected with said planet carrier assembly member ofsaid fourth planetary gear set; said sun gear member of said firstplanetary gear set being continuously connected with a stationarymember; a first interconnecting member continuously connecting saidplanet carrier assembly member of said first planetary gear set withsaid sun gear member of said second planetary gear set; a secondinterconnecting member continuously connecting said ring gear member ofsaid first planetary gear set with said ring gear member of said thirdplanetary gear set; a third interconnecting member continuouslyconnecting said planet carrier assembly member of said second planetarygear set with said planet carrier assembly member of said thirdplanetary gear set and with said ring gear member of said fourthplanetary gear set; a first torque-transmitting device selectivelyconnecting said ring gear member of said second planetary gear set withsaid stationary member; a second torque-transmitting device selectivelyconnecting said planet carrier assembly member of said first planetarygear set with said planet carrier assembly member of said fourthplanetary gear set; a third torque-transmitting device selectivelyconnecting said ring gear member of said second planetary gear set withsaid sun gear member of said third planetary gear set; a fourthtorque-transmitting device selectively connecting said sun gear memberof said third planetary gear set with said sun gear member of saidfourth planetary gear set; a fifth torque-transmitting deviceselectively connecting said sun gear member of said third planetary gearset with said planet carrier assembly member of said fourth planetarygear set; and said five torque-transmitting devices being engaged incombinations of two to establish eight forward speed ratios and onereverse speed ratio between said input member and said output member.